1. The Field of the Invention
The invention relates to physical asperity testing of disk drive systems. More specifically, the present invention relates to manners of improving disk drive physical asperity testing by exact calibration of disk drive testing systems.
2. The Relevant Art
Computer systems generally utilize auxiliary storage devices onto which data can be written and from which data can be read for later use. A direct access storage device is a common auxiliary storage device which incorporates rotating magnetic disks for storing data in magnetic form on concentric, radially spaced tracks on the disk surfaces. Transducer heads driven in a path generally perpendicular to the drive axis are used to write data to the disks and to read data from the disks. Many aspects of development and manufacturing in the disk drive industry are involved in the effort to produce the most reliable direct access storage device possible while maintaining a reasonable price. These efforts include design, component selection, development tests, and manufacturing tests. Once produced, disks are generally submitted to a variety of manufacturing tests. For instance, a series of testing operations are typically carried out on each disk. These operations may be conducted at a common station, or the disk may be transported to different stations to perform the specified operation.
One such operation involves conditioning the disk surface. The conditioning involves abrasive objects wiping or dragging across the surface of the disk. The purpose of this operation is to remove any residue or physical asperities. A further operation is a glide height test. The glide height is the height of a flying head sensor over the surface of the disk. The glide height is measured with the use of a test head gimble assembly (HGA) flying above the disk. In manufacturing, the designated glide height is designated to be at a height of or above the highest asperity on the disk. To determine the glide height, a speed sensitive HGA is used to gauge the height of the asperities on the disk surface. The actual fly-height of the HGA is critical for gauging the height of the asperities. A further operation that is frequently conducted on the disk is a magnetic test in which the magnetic coating of the disk is tested.
The disk drive industry has been engaged in an ongoing effort to increase the densities of hard disk drives. The ultrahigh densities have allowed the disk drive industry to continually miniaturize disk drives. A common problem inherent to ultrahigh densities is the fly height of the read/write head. As the density is increased, the fly height of the read/write head is reduced. If the glide height is greater than the desired fly height, the read/write head's capability to accurately and reliably read and write data will be diminished. Thus, the glide height becomes an important measurement of the quality of the disk. In fact, glide testing is a critical test that is generally performed on all disks produced.
Glide testing detects the asperities and other abnormalities that are detrimental to the performance and reliability of the disk drive. FIG. 1 shows a schematic representation of a glide height calibration test apparatus 100 of the prior art. Shown therein are a disk 102, an HGA 104, and a calibrated asperity 106. The HGA 104 is velocity sensitive, or in other terms, the fly height of HGA 104 is dependent on the linear velocity of the disk 102. In order to determine the fly height, the velocity of the disk is reduced until the slider attached at the end of the HGA 104 makes contact with the calibrated asperity 106. A small piezoelectric ceramic crystal (not shown) is coupled to the slider. When interface is made between the calibrated asperity 106 and the slider of the HGA 104, the interface is translated into an electrical signal by the piezoelectric ceramic, and the signal is transmitted to a controlling device (not shown). At that point the fly height is calibrated to the height of the calibrated asperity 106. This is the point at which the glide height is set for the tested disk drive.
FIG. 2a illustrates the fly height 206 of a slider 105 attached to HGA 104, which is the distance between the disk 102 and the slider 105. Typically, the fly height 206 is measured from the center rail trailing edge (CRTE) of the slider 105. A fly height determination is illustrated in FIG. 2c. 
FIG. 2b illustrates an additional aspect of the glide calibration test. Shown therein is a simplified schematic block diagram illustrating the roll 208 of the slider 105. The roll 208 is defined as the difference in fly heights from one edge of the slider 105 to the opposing edge of the slider 105. For example, the left side fly height might be 22 nm and the right side might be 16 nm, resulting in a roll of 6 nm.
Several problems have arisen from calibrating the glide height in the manufacturing process. One problem associated with the glide test is the inability to measure the fly height accurately due to inadequate measurement tool accuracy and repeatability. The current process includes multiple optical fly height measurements and repeated adjustment of parts to meet the optimal fly height specification. One of the adjustments is a mechanical adjustment of the suspension of the HGA 104. This form of adjustment consequently can cause damage and yield fallout. Additionally, certain components can become unstable after adjustment and begin to creep back to their original mechanical state.
Furthermore, the manufacturing time required to perform the optical measurement and adjustment process is extensive, and the yield fallout due to the handling and the adjustment is costly. The resulting variation of fly height can be very large. With such a large variation, the calibration of the glide height results in a significant yield fallout and adds to the uncertainty of the actual fly height.
The roll 208 of FIG. 2b is critical to the testing process, because 100% of the surface of the disk 102 must be tested for physical asperities 106. Problems arise when the entire surface of the slider 105 is not utilized during the glide calibration test. If the slider 105 is not positioned perfectly level (a roll of 0 nm) then the entire surface of the slider is not available for the testing procedure. For example, for a given width of the physical asperity sensing (PAS) sensor of the slider 105, potentially only a fraction of that width is utilized in the scan of the disc 102. Accordingly, instead of incrementing the path of the slider 105 by its full width every revolution, the slider 105 is only incremented by the fraction of the width in each revolution of the disc. This inefficient arrangement results in increased testing time.
Properly determining the roll is also important in accurately determining the fly height. A fly height determination 210 is illustrated in FIG. 2c. The fly height is the height of the slider 105 above the disk surface 102 at a given velocity.
Thus, it can be seen from the above discussion that there is a need existing in the art for an improved fly height adjustment and calibration method and apparatus. Particularly, it would be advantageous to provide a fly height calibration apparatus that also has the ability to eliminate the roll of the HGA and to define the fly height of the HGA with high accuracy.